1. Field of the Invention
This invention relates to a power supply apparatus for an electric vehicle such as a motor-driven scooter. More particularly, to a power supply apparatus for an electric vehicle that can simplify insulation of a power supply line of a vehicle power supply and can reduce the cost for the insulation.
2. Description of the Background Art
It is necessary for a power supply apparatus for an electric vehicle to output a high voltage for driving an electric motor for a driving apparatus and a low voltage for driving other vehicle equipment such as general electric parts.
A conventional power supply apparatus for an electric vehicle is disclosed in the Official Gazette of, for example, Japanese Patent Laid-Open No. Hei 6-115479. This power supply apparatus uses, for example, a battery of 48 V as a main power supply and supplies this voltage as it is as a drive voltage to a driving apparatus. The voltage of the battery is lowered by a DC stabilized power supply, for example, to 12 V, which is supplied to general electric parts such as a lamp apparatus and a control apparatus. In other words, from the main power supply of the high voltage, the high voltage (48 V) is directly supplied to the driving apparatus so that a sufficient power performance may be exhibited. In addition, from the DC stabilized power supply which lowers the voltage from the main power supply a stable low voltage (12 V) is generated that is necessary for the general electric parts such as the lamp apparatus. The control apparatus is supplied stably without being influenced, even if the power supply voltage of the main power supply exhibits a significant variation, by the variation of the power supply voltage so that the lamp apparatus may keep a sufficient amount of light emission and the control apparatus may operate stably.
However, the power supply apparatus for an electric vehicle described above is not configured considering such a case that a user performs maintenance of the general electric parts. This is because the voltage difference between a power supply line for the driving apparatus and a ground line for the general electric parts has a comparatively high value of 48 V. If the power supply apparatus described above is configured considering such a case that a user performs maintenance, then the insulation of the power supply line for the drive apparatus must be strengthened totally, and this configuration is complicated and increases the cost.
Also another power supply apparatus is available wherein a DC—DC converter is used for a DC stabilized power supply in order to obtain a low voltage for operating general electric parts. However, with such a power supply apparatus as just described, since the primary side and the secondary side are isolated from each other to prevent a high voltage leak therebetween, an increased cost is required. In addition, some loss is generated by a transformer or the like disposed inside of the converter. This loss is not preferable particularly with an electric vehicle from the point of view of effective utilization and assurance of a long life of the power supply.